Discussion

A ton of moisture is moving eastward today from the central Plains into the Midwest causing significant snowfall along the way from Kansas/Nebraska to Indiana. This moisture will continue to stream eastward tonight should reach the Mid-Atlantic region late tomorrow afternoon or early evening in the form of snow. The low pressure system associated with this moisture is likely to move into southwestern PA on Sunday and then to pass over the PA/MD border and reform near the mouth of the Delaware Bay by Monday morning. This storm track is a bit farther north than previous estimates and should result in less snow and more ice across SE PA with a possible sharp gradient of snowfall accumulations in the suburbs of Philly from north-to-south. There can be a significant buildup of ice in portions of SE PA Sunday night into Monday.

Given the current projected storm track, warmer air in upper levels of the atmosphere will likely cause a changeover from the initial period of snow to sleet and freezing rain in areas north of the PA/MD border. It will be hard-pressed for temperatures to get above freezing in the region from the Philly suburbs to NYC during this storm; hence, a lot of frozen precipitation is on the way for those areas. In general, for areas north of the PA/MD border, this event will feature light snow at the onset late tomorrow afternoon, then a period of heavier snow perhaps mixed with sleet tomorrow evening then a period of sleet and freezing rain late tomorrow night and Monday morning then it all could change back to snow later Monday with accumulations possible on the back end of the storm. The Monday morning and Monday evening commutes will likely be seriously impacted by the weather in the Philly and NYC metro regions.

In general, for areas south of the PA/MD border, this event will feature light snow at the onset late tomorrow afternoon, then a brief period of heavier snow mixed with sleet tomorrow evening then a transition from snow/sleet to freezing rain to then to plain rain for later tomorrow night and early Monday. Then it could all change back to snow later Monday on the back end of the storm. Despite the fact that there will likely not be significant snow and/or ice south of the PA/MD border, slippery spots can still develop given the cold ground temperatures.

Current estimates for this complicated and tricky forecast are as follows (storm timetable from late Sunday afternoon or early evening to late Monday):

DC metro region: a coating to 2 inches of snow and ice; snow changes to sleet, freezing rain and then to plain rain before a possible winding down as snow later Monday

Southern New Jersey: a coating to 2 inches of snow and ice; snow changes to sleet, freezing rain and then to plain rain before a possible winding down as snow later Monday

City of Philly: 1-3 inches of snow and ice; snow changes to sleet and freezing rain, possibly some plain rain for awhile, there can be a serious buildup of ice, it could then change back to all snow later Monday with back end snow accumulations possible

N and W suburbs of Philly: 3-6 inches of snow and ice; snow changes to sleet and freezing rain with a significant buildup of ice possible, could then change back to all snow later Monday with back end snow accumulations possible; highest amounts in this snowfall range across western Chester County, Upper Bucks County and Upper Montgomery County

NYC metro region: 4-8 inches of snow and ice; snow changes to sleet and possibly freezing rain, some buildup of ice possible, could end as all snow on Monday with back end snow accumulations possible

N and W suburbs of NYC: 6-10 inches of snow and ice; snow mixes with sleet, some buildup of ice possible, could end as all snow on Monday with back end snow accumulations possible

No matter what happens with this storm regarding snowfall amounts, bitter cold air will follow for much of next week. In fact, there could be record-challenging cold in the Northeast US on Tuesday (with fresh snow cover), Friday and Saturday mornings with one Arctic blast immediately following the storm and then another one late next week.

Stay tuned, a slight shift in the storm track can still make a big difference.